Various charge and discharge methods and control circuits are proposed in order to stably obtain power from a battery pack.
Patent Document 1 (Japanese Unexamined Patent Publication No. 2009-232559) discloses a battery pack charge balance circuit as described below. Such a battery pack charge balance circuit includes a first balance control circuit, a second balance control circuit and a protection circuit. The first balance control circuit and the second balance control circuit are connected in series to each other between both charge and discharge terminals of a charge and discharge circuit. The first balance control circuit includes a control unit connected in parallel thereto, corresponding to a plurality of battery units. The second balance control circuit includes a first branch and a second branch which are connected in parallel to each other. Thereby, it is possible to perform a shunt on a battery unit reaching an unbalance protection startup voltage which is set in advance, and to prevent the protection circuit from starting up an over-charge protection function early. Therefore, it is possible to balance the charge of each of the battery units.
In addition, Patent Document 2 (Japanese Unexamined Patent Publication No. H09-322417) discloses a discharge method as described below. A temperature of each of a plurality of battery units is detected. An arithmetic operation of a discharge termination voltage is performed on the lowest temperature of the detected temperatures as a priority. When the lowest temperature drops, an arithmetic operation is performed so that the discharge termination voltage is corrected to be lower. When the voltage of each of the battery units is compared with the discharge termination voltage, and the voltage of any of the battery units becomes lower than the discharge termination voltage, the discharge of all the battery units is stopped. Thereby, it is possible to prevent over-discharge from occurring, and to prevent a residual capacity from running out quickly.